mm: clarify mm_struct.mm_{users,count} documentation

	unsigned long task_size;		/* size of task vm space */

	unsigned long highest_vm_end;		/* highest vma end address */

	pgd_t * pgd;

	atomic_t mm_users;			/* How many users with user space? */

	atomic_t mm_count;			/* How many references to "struct mm_struct" (users count as 1) */

	/**

	 * @mm_users: The number of users including userspace.

	 *

	 * Use mmget()/mmget_not_zero()/mmput() to modify. When this drops

	 * to 0 (i.e. when the task exits and there are no other temporary

	 * reference holders), we also release a reference on @mm_count

	 * (which may then free the &struct mm_struct if @mm_count also

	 * drops to 0).

	 */

	atomic_t mm_users;

	/**

	 * @mm_count: The number of references to &struct mm_struct

	 * (@mm_users count as 1).

	 *

	 * Use mmgrab()/mmdrop() to modify. When this drops to 0, the

	 * &struct mm_struct is freed.

	 */

	atomic_t mm_count;

	atomic_long_t nr_ptes;			/* PTE page table pages */

#if CONFIG_PGTABLE_LEVELS > 2

	atomic_long_t nr_pmds;			/* PMD page table pages */